Rotary electrical machine

ABSTRACT

A rotary electrical machine has a mechanism capable of varying an output characteristic, without increasing mechanical loss, or without consuming the electric power that does not contribute to increasing torque. The rotary electrical machine has a rotor with N pole and S pole magnets alternately and fixedly disposed thereon. An end surface, (which opposes the rotor), of each of a plurality of first teeth positioned on a first stator section is broader than that of the opposite surface thereof, and a winding is wound around a portion between both of the end surfaces. A second stator section has second teeth, corresponding the number of the first teeth, and which has no winding. The second teeth are disposed to oppose the end surfaces of the respective first teeth, and each second tooth is reciprocally movable between a reference position at which the second tooth directly opposes the respective first tooth and a maximum movable position located at the right center position between the respective end surfaces. At the reference position, a strong magnetic flux flows into the entire first tooth from each magnet. At the maximum movable position, a weak magnetic flux flows over the end surface of each first tooth. A middle amount of the magnetic flux flow occurs at a middle moved position.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 11/298,979, filed on Dec. 9, 2005, which is basedon and claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2004-357339, filed on Dec. 9, 2004; and Japanese PatentApplication No. 2005-133559, filed Apr. 28, 2005, the entire contents ofwhich is expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small rotary electrical machine inwhich a current flowing through a coil is not used for a field magnetweakening control. An extensive operation range covering a high torquelow speed rotation through a low torque high speed rotation is thusprovided, and a control thereof is easily done with high efficiency.

2. Description of the Related Art

Conventionally, radial gap type electric motors, such as a radial gaptype rotary electrical machine, are used as a drive source forelectromotive two-wheeled vehicles or the like. Such radial gap typeelectric motors, and other general electric motors, have a structure inwhich a yoke of a rotor (rotor side yoke) and a yoke of a stator (statorside yoke) oppose each other, and in which their opposing surfacesextend parallel to an axis of a rotating shaft supported by bearings.

The opposing surface of the rotor side yoke has a plurality of fieldmagnets circumferentially disposed on a cylindrical inner wall, whilethe opposing surface of the stator side yoke has a plurality of teethradially disposed thereon so as to oppose the surface of the rotor sideyoke. A coil is wound around each one of the plurality of teeth. Thatis, in the radial gap type electric motor, the opposing surfaces of thefield magnets and the teeth extend about axes transverse to the axis ofthe rotating shaft, and the opposing surfaces define an annular gaptherebetween about the rotating shaft. That is, the gap in the radialgap type electric motor is defined in a direction generally transverseto the axis of rotation.

In contrast, although being a kind of the radial gap type electricmotor, there is another electric motor that has a configuration in whichthe stator side yoke is cylindrically formed, and the rotor side yoke iscolumnar and positionable within the cylinder. One such type of electricmotor is proposed, for example, in Japanese Publication No. JP2000-261988. Such an electric motor has a cylindrical member in which apermeable section and an impermeable section are alternately positionedbetween opposing surfaces of ends of respective projections of a statorcore of the stator core side yoke and opposing surfaces of respectivepermanent magnets of the rotor side yoke to prevent cogging fromoccurring and also to bring in a low torque operation in a high speedrotation.

Another electric motor in which the stator side yoke is cylindricallyformed and the rotor side yoke is columnar to be positioned within thecylinder, is proposed, for example, in Japanese Publication No. JP2004-166369. In order to reduce the stator flux linkage in the highspeed rotation, the stator core of the stator side yoke is constructedwith a cylindrical core extending about an axis of rotation and abar-like core reciprocating within the cylindrically shaped core in adirection generally transverse to the axis of rotation. The bar-likeshaped core moves in the transverse direction of the stator corerelative to a coil that is circumferentially wound around thecylindrically shaped core.

Recently, in addition to the radial gap type rotary electrical machines,axial gap type rotary electrical machines have attracted a great deal ofattention. For example, an axial gap type electric motor, as one of theaxial gap type rotary electrical machines, has a disk-like rotor sideyoke including a rotational shaft supported by its bearings and adisk-like stator side yoke with a center aligned with an axis of therotational shaft. The disk-like rotor side yoke and disk-like statorside yoke are disposed opposite each other.

On a surface of the rotor side yoke, a plurality of field magnets arecircularly (or annularly) disposed along a disk-like circumferentialportion thereof. Likewise, a plurality of teeth is disposed along adisk-like circumferential portion of a surface of the stator side yoke.The surface of the rotor-side yoke and the surface of the stator-sideyoke are disposed opposite each other. Also, the opposing surfaces ofthe field magnets and of the teeth define a gap therebetween, and theopposing surfaces define a surface that crosses the rotational shaft atright angles (i.e., perpendicularly crosses the rotational shaft). Thatis, the gap is formed to extend in a direction along the rotationalshaft, i.e., axially.

One method to vary an output characteristic of an axial gap typeelectric motor, as thus described, includes moving either a rotor (therotor side yoke having field magnets) or a stator disposed to oppose tothe rotor (a coiled core positioned on the stator side yoke) in adirection of the rotational shaft to control a distance between therotor and the stator. Therefore, an amount of magnetic flux flowingbetween the field magnets and the coiled core is controlled. However,though conventional gap type electric motors can vary the outputcharacteristic by increasing the gap between the rotor and the stator,they necessarily require that the electric motor units be bulkier toallow for said variation in gap size. Such increased bulkiness iscontrary to the desire to have gap type electric motors (both axial gaptype and radial gap type) be as small as possible.

SUMMARY OF THE INVENTION

In view of the circumstances, an aspect of the present invention is toprovide a rotary electrical machine in which a stator disposed oppositeto a rotor is divided into at least two portions. One portion is fixedand another portion is movable in a rotational direction of the rotorrelative to the fixed portion to greatly change flow of flux, i.e., abase portion of the stator is rotational (movable) to control the field.

In accordance with one aspect of the present invention, a rotaryelectrical machine comprises a rotor rotational about an axis of arotating shaft and a stator disposed so as to oppose to the rotor. Oneof the rotor and the stator is divided into at least two portions in theaxial direction. One such portion is movable in a rotational directionor a reverse rotational direction of the rotor relative to another suchportion in such a manner that a gap to form a magnetic resistancebetween the first portion and the second portion is variable.

This rotary electrical machine is constructed, for example, such thatthe movement of the one portion relative to another portion is areciprocal movement within a predetermined angle.

The rotary electrical machine can be constructed, for example, tocomprise a rotor and a stator, the stator having a first portion and asecond portion. The first portion is a first stator core having a firstset of teeth. The first set of teeth has first end surfaces that opposethe rotor, and a winding is wound around a circumferential side surfaceof each one of the first set of teeth. The second portion of the statoris a second stator core having a second set of teeth. Each tooth of thesecond set of teeth has an end portion positioned to oppose second endsurfaces of the first set of teeth, the second end surfaces facing in anopposite direction from the first end surfaces that oppose to the rotor.

The rotary electrical machine is constructed, for example, in such amanner that a rotational angle of the second portion of the stator,relative to the first portion of the stator, is less than a pitch angledefined by two adjacent teeth of the second set of teeth.

In another mode, the rotary electrical machine can be constructed, forexample, to comprises a rotor and a stator, the rotor having a firstportion and a second portion. The first portion of the rotor is a firstrotor section having a first set of magnetic members, each of the firstset of magnetic member having a first end surface disposed opposite thestator. The second portion of the rotor is a second rotor section havinga second set of magnetic members. Each magnetic member of the second setof magnetic members have an end portion positioned opposite to secondend surfaces of the first set of magnetic members the second endsurfaces facing in an opposite direction from the first end surfaces.

The rotary electrical machine is constructed, for example, in such amanner that a rotational angle of the second portion of the rotor,relative to the first portion of the rotor, is less than a pitch angledefined by two adjacent magnetic members of the second set of magneticmembers.

In accordance with another aspect of the present invention, a rotaryelectrical machine comprises a rotor having an annular section thatrotates about an axis of a rotating shaft and a first stator core havinga first set of teeth. Each tooth of the first set of teeth has a portionwith an end surface positioned opposite to the annular section. Awinding is wound around a side circumferential surface of the portion,except for both end surfaces thereof. A second stator core has a secondset of teeth. Each tooth of the second set of teeth has an end portionpositioned to oppose second end surfaces of the first teeth, the secondend surfaces facing in an opposite direction to the end surfaces of thefirst teeth. The second stator core is movable in at least a rotationaldirection or a reverse rotational direction of the rotor.

The second stator core is constructed, for example, to be movable in therotational direction or the reverse rotational direction of the rotorand also movable in an axial direction relative to the rotor.

Also, each tooth of the first set of teeth is constructed, for example,to have a projection abutting on a side surface of each tooth of thesecond set of teeth. The projection extends from the second end surfacesof each tooth of the first set of teeth and opposite the end portions ofthe second set of teeth.

In another mode, rotary electrical machine is constructed in such amanner that each tooth of the first set of teeth is divided into a firstportion and a second portion. The first portion has a winding on acircumferential surface thereof and the second portion has no winding ona circumferential surface thereof. The second set of teeth include teethcorresponding to the first portion of each tooth of the first set ofteeth, as well as other teeth corresponding to the second portion ofeach tooth of the first set of teeth.

In another mode, respective opposing surfaces of the rotor and the firstset of teeth can be formed to extend obliquely in such a manner that aninner side of the opposing surface of the rotor that is positionedradially closer to the axis of a rotating shaft has a greater thicknessthan an outer side of the opposing surface positioned radially fartherfrom the axis.

In accordance with another aspect of the present invention, a rotaryelectrical machine comprises a cylindrical rotor rotational about anaxis of a rotating shaft and a first stator core having a first set ofteeth. Each tooth of the first set of teeth has an end surfacepositioned inside of the cylindrical configuration of the cylindricalrotor and opposite to the rotor. A winding is wound around acircumferential side surface of each tooth of the first set of teeth,except for both end surfaces of the tooth. A second stator core has asecond set of teeth. Each tooth of the second set of teeth has an endportion positioned opposite second end surfaces of the first set ofteeth. The second end surfaces face in a direction opposite from the endsurfaces of the first teeth. The rotary electrical machine isconstructed such that the second stator core is movable in a rotationaldirection or a reverse rotational direction of the rotor, and the firststator core is disposed between the cylindrical rotor and the secondstator core.

In accordance with an additional aspect of the invention, a rotaryelectrical machine comprises a columnar cylindrical rotor rotationalabout an axis of a rotating shaft. A first stator core has a first setof teeth disposed circumferentially about the rotor, each tooth of thefirst set of teeth having one end surface opposite the rotor. A windingis wound around a circumferential side surface of each tooth of thefirst set of teeth, except for both end surfaces of the tooth. A secondstator core has a second set of teeth, each tooth of the second set ofteeth having one end portion positioned opposite second end surfaces ofthe first set of teeth that face in a direction opposite to the endsurfaces of the first set of teeth. Second end portions of the secondset of teeth are retained by a retainer. The rotary electrical machineis constructed such that the second stator core is movable in arotational direction or a reverse rotational direction of the rotorabout the first stator core, and the first stator core is disposedbetween the rotor and the second stator core.

In a preferred mode, the rotary electrical machine is constructed, forexample, in such a manner that, when the second set of teeth arepositioned to directly face the first set of teeth, a magneticresistance existing between a tooth of the first set of teeth and anoppositely facing tooth of the second set of teeth is smaller than amagnetic resistance existing between adjacent teeth of the first set ofteeth. When the second set of teeth moves so that a tooth of the secondset of teeth is positioned between adjacent teeth of the first set ofteeth, a magnetic resistance passing through the tooth of the second setof teeth is larger than a magnetic resistance existing between theadjacent teeth of the first set of teeth.

In such manners that the magnetic resistances are adjustable by adistance between adjacent teeth of the first set of teeth, or by adistance between a tooth of the first set of teeth and a tooth of secondset of teeth.

In a preferred mode of the invention, the rotary electrical machine isconstructed to include a movement drive force transmitting mechanism formoving the second stator core in the rotational direction or the reverserotational direction of the rotor. In one mode, the rotary electricalmachine is constructed such that the movement of the second stator corerelative to the first stator core is a reciprocal movement within apredetermined angle in the rotational direction or the reverserotational direction of the rotor. In another mode, the rotaryelectrical machine is constructed such that the movement of the secondstator core relative to the first stator core is an intermittentlyrotational movement in the rotational direction of the rotor. In anadditional mode, the rotary electrical machine is constructed such thatthe first set of teeth and the winding are unitarily molded together. Inanother mode, the rotary electrical machine is constructed such that thesecond set of teeth and the winding are unitarily molded together.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will now be described in connection with preferred embodimentsof the invention, in reference to the accompanying drawings. Theillustrated embodiments, however, are merely examples and are notintended to limit the invention. The drawings include the following 24figures.

FIG. 1 is a side elevational view of an electromotive two-wheeledvehicle as an example of a device on which an axial gap type rotaryelectrical machine as a rotary electrical machine according to a firstembodiment of the present invention is mounted.

FIG. 2 is a cross-sectional view, showing a structure of the axial gaptype electric motor (electric motor) together with a structure aroundthe rear end of a rear arm.

FIG. 3 shows a structure of a stator of the electric motor and thecircumference thereof, as viewed from the side of the rear wheel.

FIG. 4 is an exploded perspective view, simply and comparatively showinga schematic structure of the major part of the stator with a rotordisposed to oppose the stator and a rotational shaft of the rotor.

FIG. 5( a) through (f) are schematic illustrations showing the driveprinciple of the axial gap type electric motor.

FIG. 6 is a schematic view showing a tooth opposite to both of a N polemagnet and a S pole magnet in an actual arrangement such that the N polemagnet and the S pole magnet are positioned close to each other.

FIG. 7 is an illustration for describing reasons for the limit of therotational speed of an axial gap type electric motor.

FIG. 8 schematically shows a field magnet weakening control method usedfor increasing the rotational speed of an axial gap type electric motor.

FIG. 9 is a cross sectional view, showing the axial gap type electricmotor in the first embodiment together with the structure around therear end of the rear arm.

FIG. 10 is a perspective exploded view of the axial gap type electricmotor of the first embodiment.

FIG. 11 is a perspective view, showing an assembled axial gap typeelectric motor of the first embodiment, together with a rotation controlsystem.

FIG. 12( a), (b) and (c) are illustrations showing a pivot angle and anoperation of a reciprocal movement made by a second stator section ofthe axial gap type electric motor in the first embodiment along therotational direction of the rotor relative to a first stator section.

FIG. 13( a) and (b) are schematic illustrations for describing theprinciple of the rotation control of the axial gap type electric motorof the first embodiment made in a range from a high torque low speedrotation to a low torque high speed rotation.

FIG. 14( a) through (e) are schematic illustrations for describing a gapthat causes a magnetic reluctance.

FIG. 15( a) and (b) are schematic illustrations showing a structure ofthe major part of an alternative (first one) of the axial gap typeelectric motor of the first embodiment.

FIG. 16( a) through (d) are schematic illustrations showing a structureof the major part of another alternative (second one) of the axial gaptype electric motor of the first embodiment.

FIG. 17( a) through (d) show a structure of the major part of an axialgap type electric motor of a second embodiment.

FIG. 18( a) and (b) are schematic illustrations showing an alternative,in which the opposing surfaces of the rotor and the stator, and theopposing surfaces of the stator sections, which are two portions of thedivided stator, form surfaces other than horizontal surfaces.

FIG. 19 is a cross sectional view, showing a structure of a radial gaptype electric motor according to a third embodiment.

FIG. 20 is a cross sectional view, showing a structure of a radial gaptype electric motor according to a fourth embodiment.

FIG. 21 is a perspective bottom view showing a structure of a radial gaptype electric motor according to a fifth embodiment.

FIG. 22 is a perspective bottom view showing a relationship ofdisplacement of a rotational phase between the first rotor section andthe second rotor section when the rotor makes a high speed low torquerotation in the structure of the axial gap type electric motor accordingto the fifth embodiment.

FIG. 23 is a perspective bottom view of a structure of the major part ofthe axial gap type electric motor according to a sixth embodiment.

FIG. 24 is a perspective bottom view showing a relationship ofdisplacement of the rotational phase between the first rotor section andthe second rotor section when the rotor makes a high speed low torquerotation in the structure of the axial gap type electric motor accordingto the sixth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Definitions

As used herein, a “circumferential” surface or portion is a surface orportion that in cross-section can have a variety of shapes, including,but not limited to, circular, square, rectangular, triangular, and oval.

As used herein, an “axial” direction is defined as being along an axisor parallel to an axis. For example, an electric motor with a rotor thatrotates about an axis and a stator spaced apart from the rotor in theaxial direction defines an axial gap between the rotor and stator alongthe axis of rotation.

As used herein, “rotational direction” is defined as a direction aboutan axis. For example, a rotor that extends about an axis of rotationthereof can rotate in a rotational direction about the axis.

Electromotive Two-Wheeled Vehicle on which a Rotary Electrical Machineis Mounted

FIG. 1 is a side elevational view of an electromotive two-wheeledvehicle as an example of a device having an axial gap type rotaryelectrical machine thereon according to a first embodiment. As shown inFIG. 1, the electromotive two-wheeled vehicle of this embodiment has ahead pipe 2 disposed at a forward end of a vehicle body. A steeringshaft (not shown) for changing a direction of the vehicle body isinserted into the head pipe 2 for pivotal movement of a front wheel 7.

A handlebar supporting portion 4 to which handlebars 3 are fixed isattached to a top end of this steering shaft, and a grip 5 is attachedto each end of the handlebars 3. Also, in FIG. 1, the grip on the righthand side of the handlebars 3 forms a rotational throttle grip.

A front fork 6 having right and left members is coupled with a bottom ofthe head pipe 2 and extends downward. The members of the front fork 6have a front axle 8 interposed therebetween in suspended condition forsupporting and damping the front wheel 7.

The foregoing handlebar supporting portion 4 has indicators 9 disposedin front of the handlebars 3. A head lamp 11 is fixed on the handlebarsupporting portion 4 below the indicators 9. Flasher lamps 12 (one ofthe flasher lamps 12 positioned on the right hand side) are positionedon both sides of the head lamp 11.

Right and left members of a vehicle body frame 13 are generally L-shapedand extend rearward relative to the vehicle body. Each member of thevehicle body frame 13 is preferably a round pipe that obliquely extendsdownward and rearward from the head pipe 2 and then extends horizontallyand rearward to provide the generally L-shaped configuration of thevehicle body frame members 13.

A pair of right and left seat rails 14 are coupled with respective rearside ends of the members of the vehicle body frames 13 to furtherobliquely extend rearward and upward from the respective rear side endsof the vehicle body frame members 13. A rear end 14 a of each seat rail14 curves rearward along the same configuration of a seat 15.

A battery 16 is detachably disposed between the right and left seatrails 14. This battery 16 is constructed to incorporate a plurality ofsecond cells which are rechargeable. A seat stay 17 having a reversedU-shape is welded to a portion of the right and left seat rails 14adjacent to the curved portions of the seat rails 14. The seat stay 17slants upward forward relative to the vehicle body. The seat 15 ispositioned on the seat stay 17 and the pair of the right and left seatrails 14 such that the seat 15 can move between opening and closingpositions with the forward end of the seat 15 capable of pivotingvertically.

Also, a rear fender 18 is attached to the rear ends of the seat rails14, and a tail lamp 19 is attached to a rear surface of the rear fender18. Further, flasher lamps 21 (one of the flasher lamps 21 positioned onthe right hand side are positioned on both sides of the tail lamp 19.

Right and left rear arm brackets 22 (in FIG. 1, only the bracket 22 onthe left hand side of the vehicle is shown) are welded to a horizontalportion of each one of the right and left vehicle body frame members 13,which extend below the seat 15. A forward end of a rear arm 23 issupported by the right and left rear arm brackets 22 so as to allow avertical swing movement of the arm 23 via a pivot shaft 24.

A rear wheel 25, which preferably serves as a drive wheel, is supportedfor rotation at a center of a generally circularly formed rear end 23 aof the rear arm 23. The rear arm 23 and the rear wheel 25 are suspendedby a rear shock absorber 26 to dampen vertical movement of the wheel 25.

A pair of right and left footsteps 27 (in FIG. 1, only the footstep 27on the left hand side of the vehicle is shown) are disposed below therespective horizontal portions of the right and left vehicle body framemembers 13. Also, a side stand 28 is supported by the rear arm 23 on theleft hand side of the vehicle body via a shaft 29. This side stand 28 isurged by a return spring 31 toward a retracted position.

A drive unit including an axial gap type electric motor 32 that isarranged so as to drive the rear wheel 25 is incorporated within therear end 23 a of the rear arm 23.

Basic Structure of Axial Gap Type Electric Motor

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1, showinga structure of the axial gap type electric motor (hereunder, simply canbe called electric motor), together with a structure around the rear end23 a of the rear arm 23. However, the rear wheel 25 is not shown.

In FIG. 2, a drive unit 33 is incorporated within a space defined insideof a gear cover 34 attached to a right side (in FIG. 2) of the rear end20 a of the rear arm 23. The drive unit 33 includes the electric motor,a planetary geared speed reducer 35, a controller 36 and so forthtogether unitarily built in.

As shown in FIG. 2, the electric motor includes a rotor 38 supported bybearings 37 a, 37 b at the rear end 23 a of the rear arm 23 for rotationabout a center axis BO of the bearings 37 a, 37 b. The electric motoralso includes a generally annular (or doughnut-like shaped) stator 39fixed to an inside surface of the rear end 23 a of the rear arm 23opposite the rotor 38.

As shown in FIG. 2, the rotor 38 has a rotor side yoke 41 (41 a-41 e)which has a generally gambrel-like shape convex toward the rear end 23 aof the rear arm 23. That is, the rotor side yoke 41 includes an annularsection 41 a opposite to the stator 39. A tapered section 41 b extendsgenerally in a truncated cone shape toward the rear end 23 a of the reararm 23 from an inner circumferential periphery of the annular section 41a. A first cylindrical section 41 c coaxially extends along the centeraxis BO toward the rear end 23 a of the rear arm 23 from a terminal endof the tapered section 41 b. An annular section 41 d extends in a radialdirection toward the center axis BO from a terminal end (in FIG. 2,bottom end) of the cylindrical section 41 c. A second cylindricalsection 41 e coaxially extends along the center axis BO toward the rearend 23 a of the rear arm 23 from an inner circumferential periphery ofthe annular section 41 d.

The second cylindrical section 41 e is supported by the bearings 37 a,37 b for rotation about the center axis BO, so as to form a rotationalshaft of the rotor 38. Thus, a rotational center of a rotational shaft43 of the rotor 38 corresponds to the center axis BO of the bearings 37a, 37 b.

The rotor 38 also has a plurality of field magnets 42 fixedly positionedon a surface of the annular section 41 a of the rotor side yoke 41, saidsurface facing the stator. These field magnets 42 are located annularlyand coaxially about the center axis BO and circumferentially along theannular section 41 a. The field magnets 42 are positioned in such amanner that the N pole and the S pole alternate about the circumferenceof the annular section 41 a. Alternatively, the field magnets 42 can bemade from a single magnet member having the N pole and the S polealternately magnetized, both of which are formed with dielectric bodyportions that are permanently polarized along the same circumferentialsurface of a disk or ring.

The toothed rotational shaft 43 is fixedly attached to a rear wheel sideend of the second cylindrical section 41 e of the rotor 38, so as toextend coaxially with the rotor 38 (the second cylindrical section (41e). Thus, the toothed rotational shaft 43 rotates together with therotor 38.

A planetary gear speed reducer 35 is coupled with the toothed rotationalshaft 43 and is disposed in the tapered section 41 b of the rotor sideyoke 41. The planetary gear speed reducer 35 and the electric motor (therotor 38 and the stator 39) overlap with each other in a width directionof the vehicle.

The planetary gear speed reducer 35 is coupled with a rear axle 44 whichextends coaxially with the toothed rotational shaft 43. The planetarygear speed reducer 35 operates to reduce a speed of rotation of theelectric motor (e.g., rotation of the second cylindrical section (41 e),as well as to transmit the rotation of the electrical motor to the rearaxle 44 through the toothed rotational shaft 43.

A nut 45 is detachably screwed onto a tip 44 a of the rear axle 44 thatprojects from the gear cover 34 for the rear axle 44. The rear wheel 25,shown in FIG. 1, is fixedly attached to the rear axle 44 via the nut 45.

FIG. 3 shows a structure of the stator 39 of the electric motor and thecircumference thereof as seen from the side of the rear wheel 25. Thatis, in FIG. 3, the front side of the illustration corresponds to a righthand side of the vehicle body of the electromotive two-wheeled vehicle1, the left side of the illustration corresponds to a lower side of thevehicle body, the upper side of the illustration corresponds to a rearside of the vehicle body, and the lower side of the illustrationcorresponds to a front side of the vehicle body.

In FIG. 3 (see FIG. 2 also), the stator 39 is fixedly positioned at therear end 23 a of the rear arm 23, and includes a stator side yoke 46.The stator side yoke 46 has a lamination layer structure in which, forexample, circular steel sheets are laminated in the center axisdirection. The stator side yoke 46 has a reversed C shape around thecenter axis BO. In other words, the stator side yoke 46 has a circularshape, one portion of which is cut away.

The stator side yoke 46 of the stator 39 has generally rectangular toothreceiving openings, which number is multiples of three,circumferentially extending about the stator side yoke 46. The stator 39has teeth 47 fixedly positioned in the respective tooth receivingopenings with a lower portion of each tooth 47 inserted into therespective recess of each tooth receiving opening. The teeth 47 arecircumferentially arranged on the stator side yoke 46 at regularintervals (circumferential pitches).

Each tooth 47 is preferably a lamination layer of steel sheets, and isplaced such that a top end (see FIG. 3) thereof is spaced apart from therespective field magnets 42 of the rotor 38 in the axial direction ofthe rotational shaft 43, so that each tooth 47 opposes the field magnets42.

The circumferential pitch is an angle defined by line segments extendingbetween the center axis BO and centers of adjacent top ends of the teeth47.

The stator side yoke 46 that fixedly holds the teeth 47 is shaped as acircle, which center is consistent with the center axis BO and oneportion of which is cut away, as described above. Thus, the teeth 47,which number is multiples of three, are arranged along the circularconfiguration of the stator side yoke 46. Thereby, teeth of three phases(e.g., U phase, V phase and W phase), corresponding to the cut-awayportion of the circle, are omitted. Hereunder, the cut-away portion ofthe circle is called a teeth omitted portion 48.

The stator 39 includes a coil 49 (see FIG. 2) wound around each tooth47. The stator 39 also includes a molded section 51 in which therespective teeth 47 and the coils 49 are molded with resin or the like,and a plurality of flanges 52 formed on an circumferential outer surfaceof the molded section 51.

As shown in FIG. 3, each flange 52 has a bolt hole for attaching themolded section 51, including the teeth 47 and the coils 49, to the rearend 23 a of the rear arm 23. Bolts inserted into the bolt holes arescrewed onto the rear end 23 a of the rear arm 23 to fixedly positionthe stator 39 on the rear end 23 a of the stator 39.

Also, an inverter 54, which can supply electric power to the stator 39by being electrically connected to the stator 39, is fixed to the teethomitted portion 48 through an elastic material, (not shown) made ofrubber or the like. Further, an encoder substrate 55 is disposed in theteeth omitted portion 48. This encoder substrate 55 and the inverter 54are electrically coupled with each other through a wire harness 56 thatis preferably covered with a flexible coating (a flexible substrate orthe like can replace the harness).

Magnetic pole detecting elements 57 a, 57 b and 57 c, such as a Hallsensor, for example, are mounted on the encoder substrate 55. Themagnetic pole detecting elements 57 a, 57 b and 57 c are placed atpositions where those elements detect a moment when each electricalangle of the U phase, V phase and W phase of the electric motor reaches180 degrees (for example, when a coil current is the maximum).

FIG. 4 is a perspective view, showing a schematic structure of the majorpart of the stator 39 of FIG. 3, together with the rotor 38 placed tooppose to the stator 39, and the rotational shaft 43 thereof. The coil49 shown in FIG. 2, the molded portion 51 shown in FIGS. 2 and 3, andthe flanges 52, the inverter 54, the encoder substrate 55 shown in FIG.3, and so forth, are omitted from FIG. 4.

As shown in FIG. 4, on the stator side yoke 46, the respective recesses58, each of which is formed in a generally rectangular shape and inwhich the respective tooth 47 is inserted and fixed, are arranged in thecircular configuration. FIG. 4 also shows the portion of the stator 3 awhich is cut away at the circular pitches. A pair of shorter side innersurfaces 58 a, 58 b of each insert hole are adapted to face toward thecenter axis BO.

Further, a steel sheet portion next to each insert hole, and positionedbetween a circumferential outer surface 46 a of the stator side yoke 46and an inner side surface 58 b located closer to the circumferentialouter surface 46 a, is cut to make a slit 59 radially extending betweenthe inner surface 58 b and the outer surface 46 a.

The respective teeth 47, three of which form one set of the U phase, Vphase and W phase to which a two-pole/three-phase alternating current isapplied, are sequentially positioned on the stator side yoke 46 exceptfor the teeth omitted portion 48. Even number of the field magnets 42having the polar pair of the N pole and the S pole are disposed on therotor 38 at regular intervals corresponding to the intervals of the setof the three phases.

Of course, as described above, the field magnets 42 can be formed from asingle magnet member having the N pole and the S pole alternatelymagnetized, both of which are preferably formed with dielectric bodyportions that are permanently polarized along the same circumferentialsurface of a disk or ring.

That is, for example, the field magnets 42 are positioned in such amanner that either four field magnets 42, each having a polar pair, orone field magnet having four polar pairs oppose to a range involvingarrangement intervals of six teeth 47 at all times. Also, the fieldmagnets 42 are positioned in such a manner that either six field magnets42 each having a polar pair, or one field magnet having six polar pairs,oppose a range involving arrangement intervals of nine teeth 47 at alltimes.

Incidentally, FIG. 4 shows fifteen teeth 47 in total. Originally, thestator can have 18 teeth 47. However, three of them are omitted toallocate the encoder substrate 55 of FIG. 3.

Thus, the electric motor is constructed in such a manner that the fieldmagnets 42, each having 12 polar pairs, oppose a range involvingarrangement intervals of fifteen teeth 47 (including the omitted portionfor three teeth) at all times, whether odd number of field magnets 42are used or one field magnet is used.

Drive Principle of an Axial Gap Type Electric Motor

Next, a drive principle of the axial gap type electric motor constructedas described above is described.

FIGS. 5( a) to (f) are illustrations for describing the drive principleof the axial gap type electric motor. In FIG. 5( a), the arrow “a”indicates a rotational direction of the rotor 38, while the arrow “b”indicates the positive direction of magnetic fluxes, when a direction ofthe magnetic fluxes coming from the N pole field magnet 42 (hereunder,simply called magnet 42) is selected to be positive, and a direction ofthe magnetic fluxes coming from the S pole magnet 42 is selected to benegative. However, all the fluxes do not flow right downward asindicated by the arrow “b,” and some of them flow obliquely downward.The arrow “b” thus is given to mean that generally the magnetic fluxesflow downward.

Also, the arrow “c” indicates the positive direction of magnetic fluxes,when a direction of magnetic fluxes having the N polarity, which aregenerated in the coils 49 wound around the respective teeth 47 of thestator 39, with a current being supplied to the coils 49 and exited bythe teeth 47 (47 u, 47 v and 47 w) that are core members, is decided tobe positive, and a direction of magnetic fluxes having the S polarity isdecided to be negative. However, all the fluxes do not flow rightdownward as indicated by the arrow “b,” and some of them flow obliquelydownward. The arrow “b” thus is given to mean that generally the fluxesflow downward.

Also, in FIGS. 5( a) to (f), the teeth 47 of the U phase are indicatedby reference numeral 47 u, the teeth 47 of the V phase by 47 v, and theteeth 47 of the W phase by 47 w.

FIG. 5( a) shows a condition under which the N pole magnets 42 arepositioned right above the U phase teeth 47 u, while the S pole magnets42 are positioned between the respective V phase teeth 47 v and therespective W phase teeth 47 w.

Under this condition, a current toward the coils 49 of the U phase teeth47 u is shut down, no magnetic flux is generated in the teeth 47 u, andthe magnetic fluxes from the N pole magnets 42 flow through the teeth 47u.

A current that can generate magnetic fluxes having the S polarity flowsthrough the coils 49 of the V phase teeth 47 v, and the teeth 47 vexcites the S pole magnetic fluxes. The excited S pole magnetic fluxesof the teeth 47 v repel the S pole magnets 42, i.e., the same polemagnets, in the direction of the arrow “a.”

On the other hand, a current that can generate N pole magnetic fluxesflows through the coils 49 of the W phase teeth 47 w, and the teeth 47 wexcite the N pole magnetic fluxes. The excited N pole magnetic fluxes ofthe teeth 47 w attract the S pole magnets 42, i.e., the opposite polemagnets, in the direction of the arrow “a.”

The rotor 38 rotates in the direction of the arrow “a” by the torquetoward the direction of the arrow “a” caused by the force of repulsionand the force of attraction, and transfers to a condition shown in FIG.5( b). That is, the N pole magnets 42 are positioned between therespective U phase teeth 47 u and the respective V phase teeth 47 v,while the S pole magnets 42 are positioned right above the W phase teeth47 w.

Under this condition, the direction of the current is changed togenerate N pole magnetic fluxes in the coils 49 of the U phase teeth 47u. The teeth 47 u excite the N pole magnetic fluxes, and the excited Npole magnetic fluxes repel the N pole magnets 42, i.e., the same polemagnets, in the direction of the arrow “a.”

On the other hand, the direction of the current is changed to generate Spole magnetic fluxes in the coils 49 of the V phase teeth 47 v. Theteeth 47 u excite the S pole magnetic fluxes, and the excited S polemagnetic fluxes attract the N pole magnets 42, i.e., the opposite polemagnets, in the direction of the arrow “a.”

Also, the current toward the coils 49 of the W phase teeth 47 w is shutdown, no magnetic flux is generated in the teeth 47 w, and the magneticfluxes from the S pole magnets 42 flow through the teeth 47 w.

Also under this condition, the rotor 38 rotates in the direction of thearrow “a” by the torque toward the direction of the arrow “a” caused bythe force of repulsion and the force of attraction, and transfers to acondition shown in FIG. 5( c). Relationships between the teeth 47 andthe magnets 42 under the condition are the same as those which shown inFIG. 5( a). However, each relationship between the respective tooth 47and the respective N pole and S pole magnets 42 is shifted one by one inthe direction of the arrow “a.”

That is, the N pole magnets 42 are positioned right above the V phaseteeth 47 v, while the S pole magnets 42 are positioned between therespective W phase teeth 47 w and the respective U phase teeth 47 uwhich is one of the neighboring sets of the three phases.

The current of the teeth 47 v, the teeth 47 w and the neighboring teeth47 u, and the polarity of the magnetic fluxes generated in the coils 49under the condition of FIG. 5( c) is the same as the current of theteeth 47 u, the teeth 47 v and the teeth 47 w of sets of the threephases, and the polarity of the magnetic fluxes generated in the coils49 under the condition of FIG. 5( a), respectively.

That is, under the condition, the torque in the direction of the arrow“a” is generated by the repulsive force and the attractive force, andthe rotor 38 rotates in the direction of the arrow “a” by the torque andtransfers to a condition shown in FIG. 5( d). The relationships betweenthe teeth 47 and the magnets 42 under the condition is the same as thosewhich shown in FIG. 5( b). However, also under this condition, eachrelationship between the respective tooth 47 and the respective one ofthe N pole and S pole magnets 42 is shifted one by one in the directionof the arrow “a.”

That is, the N pole magnets 42 are positioned between the respective Vphase teeth 47 v and the respective W phase teeth 47 w, while the S polemagnets 42 are positioned right above the U phase teeth 47 u which isone of the neighboring sets of the three phases.

The current of the teeth 47 v, the teeth 47 w and the neighboring teeth47 u, and the polarity of the magnetic fluxes generated in the coils 49under the condition of FIG. 5( d) is the same as the current of theteeth 47 u, the teeth 47 v and the teeth 47 w of the sets of the threephases, and the polarity of the magnetic fluxes generated in the coils49 under the condition of FIG. 5( b), respectively.

Hereunder, similarly, the rotor 38 transfers to a condition of FIG. 5(e), and further transfers to a condition of FIG. 5( f). The N polemagnets 42 thus are positioned between the respective W phase teeth 47 wand the respective teeth 47 u of the sets of the three phases. One driverelationship, which is shown on the left hand side of FIG. 5( a),between one set of the three phases including the U phase teeth 47 u, Vphase teeth 47V and W phase teeth 47 w and the pair of N pole magnet 42and S pole magnet ends.

Continuously, again, as shown in FIG. 5( a), another drive relationshipbetween another one set of the three phases including the U phase teeth47 u, V phase teeth 47V and W phase teeth 47 w and another pair of Npole magnet 42 and S pole magnet neighboring the pair of N pole magnet42 and S pole magnet, the foregoing relationship of which has ended, andpositioned upstream of the former pair, starts as shown in FIGS. 5( a)to (f).

Additionally, in the description of FIGS. 5 (a) to (f), the positioningrelationships between the magnets 42 and the teeth 47 are divided intosix stages for easy understanding. Actually, however, the currentapplied to the coils 49 is preferably is in the form of a sine curvethat is sequentially applied to three teeth 47 of each set of the threephases neighboring each other at regular phase differences. Thedirection and magnitude of the magnetic fluxes generated in the coils 49by the applied current vary because the magnets 42 of the rotor rotate.

Also, respective distances between the N pole and S pole magnets 42 inan actual arrangement are shorter than those which are shown in FIGS. 5(a) to (f), and one tooth 47 can oppose both of the N pole magnet 42 andthe S pole magnet 42. Additionally, if a single magnet having multiplepolar pairs is used instead of the odd number of magnets 42, the N poleand the S pole contact with each other without having spacetherebetween.

The relationship shown in FIGS. 5( a) to (f) is sequentially shifted inthe rotational direction to one another among all the sets of the threephases of the teeth 47 and the pairs of two magnets 42 in associationwith neighboring teeth and magnets. That is, two teeth of the set ofthree phases of teeth 47 and one tooth of the neighboring set of threephases of teeth 47 makes a next set of three phases, and one magnet ofthe pair of two magnets 42 and one of the neighboring pair of twomagnets 42 makes a next pair of magnets.

The current for changing the directions of the magnetic fluxes of thecoils is changed under the control of the inverter 54, and a timing ofcurrent application is given also under the control of the inverter 54based upon the detection of rotational positions of the N pole magnet 42and the S pole magnet 42 by the magnetic pole detecting elements 57 a,57 b and 57 c shown in FIG. 3.

As thus described, magnetic circuits are made between the rotor 38 andthe stator 39 in the axial gap type motor. The excitation of therespective teeth 47 of the stator 39 is sequentially changedcorresponding to the N pole and S pole of the magnets 42 of the rotor 38via the coils wound around the respective teeth 47, thereby rotating therotor 38 using the repulsive force and the attractive force of themagnets 42 of the rotor 38 against the excitation of the respectiveteeth 47.

FIG. 6 is an illustration, showing that one tooth 47 opposes both of theN pole magnet 42 and the S pole magnet 42 in an actual arrangement insuch a manner that the N pole magnet 42 and the S pole magnet 42 arepositioned close to each other. In this illustration, the arrow “a”again indicates the rotational direction of the rotor 38. Also, adirection of the magnetic fluxes flowing between the N pole magnet 42and the S pole magnet is indicated by arrows G1, G2 and G3. Further,this condition is the same as the condition occurring transitionallywhen the conditions shown in FIGS. 5( a) to (f) are shifted to oneanother.

In FIG. 6, a current flows through the coil 49 wound around the tooth 47on the stator 39 counterclockwise in a top plan view as indicated by anarrow E. Therefore, magnetic fluxes generated in the coil 49 and excitedby the tooth 47 flow as indicated by an arrow G4, and cross the magneticfluxes flowing between the N pole magnet 42 and the S pole magnet 42. Onthis occasion also, the N pole magnet 42 repels and the S pole magnet 42attracts to generate the torque in the rotor 38 in the direction of thearrow “a.”

In FIG. 6, when the magnets 42 move to other positions relative to thetooth 47, and the magnet 42 on the left hand side is replaced by the Npole magnet and the magnet on the right hand side is replaced by the Spole magnet, the direction of the current that is given to the tooth 47is reversed from the direction indicated by the arrow E, i.e., thedirection is changed to the clockwise direction in view of the top sideof the illustration.

By the way, in the electric motor having the basic structure describedabove, the rotational power thereof does not become larger than acertain limit because of a structural restriction in its rotationalspeed. If converted into a speed of a motorcycle, approximately 20 kmper hour is a limit in order to obtain a torque that is necessary forthe vehicle, shown in FIG. 1, to run. However, it is understood that thedata can vary in accordance with diameters of tires, gear ratios ofdrive gear systems, specifications of motors and so forth.

FIG. 7 is an illustration to describe reasons for the limit of therotational speed of a normal electric motor. FIG. 7 shows positioningconditions of the N pole magnet 42, the V phase tooth 47 v and othersaround them shown in FIG. 5( c).

Additionally, FIG. 7 only shows the coil 49 for the V phase tooth 47 v,and omits the coils for the other teeth. As described with reference toFIG. 5, no current is applied to the coil 49 when the magnet 42 ispositioned right above the tooth 47.

In FIG. 7, the rotor 38, the stator 39, and teeth 47 (47 u, 47 v and 47w) are preferably made of a soft magnetic material. Because a distance“d” between the opposing surfaces of the magnet 42 and the tooth 47 isextremely small, a space magnetic resistance is low. Thus, the magneticfluxes flowing between the N pole magnet 42 (N) and S pole magnet 42 (S)are divided into two portions. One portion is a magnetic flux flow 61while another portion is a magnetic flux flow 62, both of which flowthrough the magnetic poles of the magnets 42, the rotor 38, the teeth 47and the stator 39.

Thus, larger magnetic fluxes involving the foregoing two magnetic fluxflows 61 and 62, both of which merge together, pass through the coil 49via the tooth 47 v positioned within the coil 49.

While the rotor 38 rotates in the direction of the arrow “a,” a currentis generated in the coil 49, according to the Faraday's electromagneticinduction law, because the fluxes passing through the coil 49 cross thecoil 49. The current generated in the coil 49 in turn generates magneticfluxes having the S polarity from the coil 49. That is, the S polemagnetic fluxes generated in the coil 49, i.e., in the tooth 47, by thecurrent generated in the coil 49 functions to attract the N pole magnet42 (N).

In other words, resistive force (magnetic resistance) affects therotation of the rotor 38. The faster the rotation of the rotor 38, thefaster the speed of the magnetic fluxes, which involves the foregoingtwo magnetic flux flows 61 and 62 merging together in the coil 49, andcrossing the coil 49. The faster the speed of the magnetic fluxescrossing the coil 49, the larger the current generated in the coil 49.The larger the current generated in the coil 49, the larger the amountof the magnetic fluxes generated in the tooth 47 v by the current toincrease the magnetic resistance of the rotor 38. Before long, theincreased magnitude of the rotational power of the rotor 38 and themagnetic reluctance reach a balance with each other. This balancedcondition is the limit of the rotational speed described above. Ofcourse, the limit can go up with an increase of the electric supply.However, it is not a good plan because the consumption of theelectricity increases in geometric progression.

As a method of improving the weak point of the rotational characteristicof the axial gap type electric motor to increase the rotational power,i.e., a method of shifting the rotational condition to a low torque highspeed rotation from the high torque low speed rotation, a field magnetweakening control method is used.

FIG. 8 is an illustration, schematically showing the field magnetweakening control method. Under the condition such that no current isapplied to the coil 49 when the N pole magnet 42 (as to S pole magnet42, the same) is positioned right above the tooth 47 as described withreference to FIG. 7, a large resistance affects the rotation of therotor 38 when the rotational speed increases.

As shown, however, if a moderate current is applied to the coil 49 inthe direction indicated by the arrow E when the N pole magnet ispositioned right above the tooth 47 (as to S pole magnet 42, reversedirection), magnetic fluxes having the N polarity are generated in thedirection indicated by the arrow G4 (as to S pole magnet 42, reversedirection). The magnetic fluxes generated by this coil function toweaken the N pole magnetic fluxes that go to the tooth 47 from the Npole magnet 42 as indicated by the arrow G2. That is, because themagnetic fluxes function to weaken the magnetic flux flows 61 and 62shown in FIG. 7, the magnetic resistance decreases and the rotationalpower becomes large, corresponding to the weakened magnetic flux flows.Namely, the low torque high speed rotation can be realized.

In the field magnet weakening control method, a new current having aphase that is inconsistent with the phase of the alternating currentapplied to the tooth 47 having three phases (U phase, V phase and Wphase) is applied when the electromagnets 42 are positioned right abovethe teeth 47 and the current becomes zero. That is, a current thatgenerates magnetic fluxes in the direction of weakening the magneticfluxes going to the coils 49 from the electromagnets 42, when thecurrent becomes zero, is further added to a current for generatingrotation (for generating torque) that is applied to the coil 49. Inother words, a current that does not contribute to the rotational torqueitself is newly applied.

Additionally, as a method to realize the low torque and high speedrotation of the electric motor, there is another method to enlarge theopposing distances of the rotor and the stator in the rotationaldirection (i.e., to enlarge the magnetic gaps between the rotor and thestator), as described above. However, the flow of the magnetic flux flowwas unstable in the magnetic gaps between the rotor and the stator.

Described below are portions at which the flow of the magnetic flux flowis in good order, and how to control the flow of the magnetic flux flowusing variable magnetic gaps. As a result, improved controllability ofthe output characteristic of the electric motor is achieved.

Structure and Operation of an Axial Gap Type Electric Motor According toa First Embodiment

Based upon the basic structure and the drive principle of the foregoingaxial gap type electric motor, a structure and an operation of an axialgap type electric motor according to a first embodiment is described.

FIG. 9 is a cross sectional view, showing an axial gap type electricmotor according to the first embodiment together with the structurearound the rear end of the rear arm. Additionally, in FIG. 9, the sameconstructive portions as those shown in FIG. 2 are assigned with thesame reference numerals and symbols as those used in FIG. 2.

FIG. 10 is a perspective exploded view of the axial gap type electricmotor according to the first embodiment. Hereunder, with reference toFIGS. 9 and 10, the structure of the axial gap type electric motor(hereunder, simply called electric motor) of the present embodiment isdescribed.

First, the electric motor 70 of the present embodiment has a rotor 71.The rotor 71 is constructed so as to rotate about an axis of arotational shaft 72 like a disk. The rotor 71 has the same structure asthe rotor 38 shown in the basic structure of FIGS. 2 and 4.

That is, in FIG. 10, the rotor 71, the rotational shaft 72, a rotor sideyoke 73, a annular section 74, a tapered section 75, a first cylindricalsection 76, a annular section 77, a second cylindrical section 78, andfield magnets 79 are the same as the rotor 38, the rotational shaft 41e, the rotor side yoke 41, the annular section 41 a, the tapered section41 b, the first cylindrical section 41 c, the annular section 41 d, thesecond cylindrical section (rotational shaft) 43, and the field magnets42, respectively, shown in FIGS. 2 and 4.

A stator (stator section) 88 is disposed opposite the rotor 71 (morespecifically, a surface where a plurality of field magnets 79 aredisposed). The stator 88 is divided into two portions, a first statorsection 83 and a second stator section 87.

The first stator section 83 includes a first stator core 80 having afirst set of teeth 81 retained by a retainer (not shown). The first setof teeth 81 are disposed in such a manner that one end surface 81 a ofeach first tooth 81 opposes the rotor 72 in an axial direction. Eachtooth 81 has a winding 82 wound around a circumferential side surface 81c thereof, except for both end surfaces (81 a, 81 b). Additionally, thefirst teeth 81 are formed in such a manner that the end surface 81 a ofeach tooth 81 opposing the rotor 71 is larger than an opposite endsurface 81 b. Thus, with regard to spaces between neighboring firstteeth 81, one of the spaces existing between the end surfaces 81 aopposing to the rotor 71 is narrower than the other space between theopposite surfaces 81 b.

Each first tooth 81 having the respective winding 82 is molded togetherwith the winding 82 to form the respective first stator section 83,which has a circular configuration. Additionally, a drive currentcontrol for generating torque that is applied to respective windings(coils) 82 of the first teeth 81 is the current control that uses thesame method as that described with reference to FIG. 5, i.e., the basicdrive method that does not include the field magnet weakening control.The torque of the electric motor is generated under the drive currentcontrol.

Also, the second stator section 87 itself forms a second stator core(87) with second teeth 84, which number is the same as the number of thefirst teeth 81, retained by a retainer 85. Each second tooth 84 of thesecond stator section 87 has one end portion 84 a that is positioned tooppose to the opposite end surface 81 b of the first tooth 81 of thefirst stator section 83. Another end 84 b of each second tooth 84 ispress-fitted into one of multiple tooth receiving openings 86 that areformed on the annular retainer 85. The second teeth 84 and the retainer85, which has the second teeth 84 press-fitted and fixed to the toothreceiving openings 86 therein, together form the second stator section87. Preferably, the second teeth 84 and the retainer 85 are unitarilymolded, though the mold is not shown in FIG. 10.

FIG. 11 is a perspective view showing the electric motor 70 with thestructure described above completely assembled, together with a rotationcontrol system. The molds of the first stator section 83 and the secondstator 87 are not shown in FIG. 11. Further, slits 89 which are omittedin FIG. 10 (see slits 59 of FIG. 4) are indicated in the retainer 85 ofthe second stator section 87 shown in FIG. 11.

As shown in FIG. 11, the rotor 71, the first stator section 83 and thesecond stator section 87 of the electric motor 70 shown in the explodedview of FIG. 10 are positioned in order axially along the rotationalaxis so as to be slightly spaced apart from one another.

The first stator section 83 is preferably fixed to the rear end 23 a ofthe rear arm 23 shown in FIG. 2 by an engaging section formed at themolded portion (not shown). The second stator section 87 is preferablynot completely fixed and can pivot somewhat relative to the first stator83, as described below.

As shown in FIG. 11, a pivot mechanism for the second stator section 87is constructed in such a manner that a toothed portion for gearengagement 90 is formed at a portion of a circumferential side surfaceof the retainer 85. The toothed portion 90 engages with a small diametergear of speed reduction gears 91 of a rotation control system. A largediameter gear of the speed reduction gears 91 engages with a smalldiameter gear of speed reduction gears 92 in the next stage, and a largediameter gear of the speed reduction gears 92 engages with a smalldiameter gear of speed reduction gears 93 in the third stage. A largediameter gear of the speed reduction gears 93 engages with a worm gear95 fixedly attached to the tip of a rotational shaft of an electricmotor 94.

The motor 94 is connected to a drive pulse voltage output terminal,which is not shown, of a controller 97 to which electric power fordriving circuits is supplied from a power source 96. An axis of rotationof the motor 94 in the right and reverse directions is changed to extendat right angles to its original direction by the worm gear 95. Also, therotation is reduced in speed and is transmitted to the large diametergear of the speed reduction gears 93. The rotation is reduced throughthree stages, corresponding to gear ratios between the reduction gears93, 92 and 91, in order, and then transmitted to the toothed portion 90.

Accordingly, the second stator section 87 is constructed to be slightlymovable in the rotational direction of the rotor 71 relative to thefirst stator section 83. That is, the second stator section 87 cancontinuously, intermittently and reciprocally move with a narrow pivotangle. In other words, the second stator section 87 can move steplessly,intermittently, and slightly in both the right and reverse directionsalong the rotational direction of the rotor 71.

FIGS. 12( a), (b) and (c) are illustrations for describing the pivotangle and the operation of the reciprocal movement made by the secondstator section 87 along the rotational direction of the rotor 71relative to the first stator section 83. Additionally, in FIGS. 12(a),(b) and (c), in order to simply show transitional conditions of thesecond teeth 84 of the second stator section 87 relative to the firstteeth 81 of the first stator section 83, the windings 82, the slits 89and the toothed portion 90 for gear engagement, the rotation controlsystem etc. shown in FIG. 11 are omitted in the illustrations.

FIG. 12( a) shows a positional relationship of the second teeth 84 ofthe second stator section 87 relative to the first teeth 81 of the firststator section 83, occurring when the high torque low speed rotation ismade. In this embodiment, the position in this positional relationshipis the reference position.

With the pivotal movement of the second stator section 87 describedabove, the second teeth 84 can pivot (e.g., via reciprocal movement) ina narrow angular range along the rotational direction of the rotor 71indicated by the arrow “a,” from the reference position shown in FIG.12( a), i.e., a position at which each second tooth 84 directly opposesthe respective first tooth 81, to the maximum movable position shown inFIG. 12( c), i.e., a right center position between adjacent first teeth81, by way of a midway position shown in FIG. 12( b). Additionally, themidway position shown in FIG. 12( b) is illustrative of any position inthe stepless and intermittent pivotal movement between the referenceposition and the maximum movable position.

FIGS. 13( a) and (b) are illustrations for describing the principle ofthe rotation control of the electric motor 70 in this embodiment made ina range from a high torque low speed rotation to a low torque high speedrotation. Additionally, in order to simply show, the windings 82 woundaround the respective teeth 81 and the mold are omitted in FIGS. 13( a)and (b). Similarly, the mold of the second teeth 84 and the retainer 84is omitted in the illustrations.

Also, FIG. 13( a) shows the high torque low speed rotational conditionshown in FIG. 12( a) under which each second tooth 84 directly opposesthe respective first tooth 81. FIG. 13( b) shows the low torque highspeed rotational condition shown in FIG. 12( c) under which each secondtooth 84 is at the right center position between the adjacent firstteeth 81.

FIG. 13( a) shows a condition under which the i^(th) magnet 79 i of therotor 71 directly opposes the i^(th) first tooth 811 of the first stator83 on the stator side, and the i^(th) second tooth 84 i of the secondstator section 87 on the stator side directly opposes the first tooth811. That is, FIG. 13( a) shows the same condition as that shown in FIG.12( a).

FIG. 13( b) shows a condition under which the positional relationshipbetween the magnet 79 i of the rotor 71 and the first tooth 81 i of thefirst stator section 83 is not changed from that shown in FIG. 13( a),and the second tooth 84 i of the second stator section 87 is placed atthe right center position between adjacent first teeth 81 i and 81 i+1of the first stator section 83. That is, FIG. 13( b) shows the samecondition as that shown in FIG. 12( c).

In FIG. 13( a), the annular section 74 of the rotor side yoke 73, thefirst teeth 81 (81 i−1, 81 i, 81 i+1) of the first stator section 83,the second teeth 84 (84 i−1, 84 i, 84 i+1) of the second stator section87 and the retainer 85, all belonging to the rotor 71, have strongpermeability. Also, the opposing surfaces of the magnets 79 (79 i−1, 79i, 79 i+1) and the first teeth 81, and the opposing surfaces of thefirst teeth 81 and the second teeth 84 are extremely close to eachother, respectively. Thus, a magnetic resistance “h” between theopposing surfaces of the magnets 79 (79 i−1, 79 i, 79 i+1) and the firstteeth 81, and a magnetic resistance “k” between the opposing surfaces ofthe first teeth 81 and the second teeth 84 are small.

Additionally, as described above, the end surface 81 a of each firsttooth 81 opposing to the rotor 71 is formed to be larger than the otherend surface 81 b thereof. Thus, between respective adjacent first teeth81, a magnetic resistance “j” exists between the end surfaces 81 aopposing to the rotor 71 that is extremely smaller than a magneticresistance between the other surfaces. However, this “j” magneticresistance is larger than the magnetic resistance “h” with the rotor 71.That is, there is a relationship (h≈k<j) among the magnetic resistances.

Thus, the magnetic fluxes generated between the magnet 79 i (selected tobe N pole) and the neighboring magnet 79 i−1 (S pole, accordingly)hardly permeates through the portions having the magnetic resistance“j,” and form a strong magnetic flux flow 98 a that permeates throughthe portions having the magnetic resistance “h,” the first tooth 811,the portions having the magnetic reluctance “k,” the second tooth 84 i,the retainer 85, the second tooth 84 i−1, the retainer 85, the portionshaving the magnetic resistance “k,” the first tooth 81 i−1, the portionshaving the magnetic resistance “h,” and the annular section 74.

Further, the magnetic fluxes generated between the magnet 79 i (N pole)and the other neighboring magnet 79 i+1 (S pole) hardly permeatesthrough the portions having the magnetic resistance “j,” and form astrong magnetic flux flow 98 b that permeates through the portionshaving the magnetic resistance “h,” the first tooth 81 i, the portionshaving the magnetic resistance “k,” the second tooth 84 i, the retainer85, the second tooth 84 i+1, the retainer 85, the portions having themagnetic resistance “k,” the first tooth 81 i+1, the portions having themagnetic resistance “h,” and the annular section 74.

These phenomena occur even though the magnet 79 i is not the N polemagnet but the S pole magnet, except that the magnetic fluxes flow inthe reverse direction, and similarly a strong magnetic flux flow is madethat flows through the associated magnet 79, first tooth 81, secondtooth 84, retainer 85 and annular section 74.

As described above, the strong magnetic fluxes cause the magneticresistance that can soon bring in the limit against the transition ofthe electric motor 70 to the low torque high speed rotation from thehigh torque low speed rotation without taking any measure. Also, asdescribed above, there is the field magnet weakening control to delaythe limit.

However, in the present embodiment, as shown in FIG. 11 and FIGS. 12(a), (b) and (c), the second teeth 84 can pivot (reciprocal movement) inthe narrow angular range along the rotational direction of the rotor 71indicated by the arrow “a” from the reference position at which eachsecond tooth 84 directly opposes the respective first tooth 81 to themaximum movable position located at the right center position betweenadjacent first teeth 81.

Now, suppose that the second teeth 84 pivot to the maximum movableposition shown in FIG. 13( b) from the reference position shown in FIG.13( a). On this occasion, a magnetic resistance “m,” which is largerthan the magnetic resistance “k” under the directly opposing condition,is made between the opposing surfaces of each first tooth 81 and therespective second tooth 84. Further, because each second tooth 84 ispositioned in the configuration to project from the retainer 85, amagnetic resistance “n” exists, which is larger than the magneticresistance “m” made with the second tooth 84.

That is, there is a relationship “m<N” therebetween. The magneticresistance “n” is negligible compared with the magnetic resistance “m.”Thus, under the condition shown in FIG. 13( b), it is almost true thatthe magnetic resistance made between each second tooth and the oppositeend surface 81 b of the respective first tooth 81 is “m,” when thesecond tooth 84 moves to the right center position between adjacentfirst teeth.

As described above, the end surface 81 a of each first tooth 81 opposingthe rotor 71 is formed to be larger than the other end surface 81 bthereof. Thus, between the respective adjacent first teeth 81, themagnetic resistance “j” between the end surfaces 81 a opposing to therotor 71 is extremely small, and under the condition shown in FIG. 13(b), the relationship (j<2m) exists between the magnetic resistance “j”and the magnetic resistance m.

That is, it is true that a distance (magnetic resistance “j”) definedbetween the end surface 81 a of each first tooth 81 opposing to therotor 71 and the end surface 81 a of the adjacent first tooth 81 issmaller than the minimum distance (magnetic resistance “m”) definedbetween each second tooth 84 and the opposite end surface 81 b of thefirst tooth 81.

By being brought into this condition, i.e., the condition under whichthe relationship among the magnetic resistance of the respective membersis h<j<m<n is brought, as shown in FIG. 13( b), the magnetic fluxesbetween the magnet 79 i (N pole) and the other neighboring magnet 79 i−1(S pole) form a weak magnetic flux flow 99 a that does not flow to thesecond tooth 84 i−1 or to the retainer 85 from the first tooth 81 i, dueto the magnetic resistance “m” and the magnetic resistance “n,” butpermeates through the first tooth 811, the portions having the magneticresistance “j,” the first tooth 81 i−1 and the annular section 74.

Also, the magnetic fluxes made between the magnet 79 i (N pole) and theother neighboring magnet 79 i+1 (S pole) form a weak magnetic flux flow99 a that does not flow to the second tooth 84 i+1 or to the retainer 85from the first tooth 81 i, due to the magnetic resistance “m” and themagnetic resistance “n,” but permeates through the first tooth 81 i, theportions having the magnetic resistance “j,” the first tooth 81 i+1, andthe annular section 74.

Thus, the magnetic fluxes from the magnets 79 do not cross the windings82 of the respective first teeth 81, and the magnetic resistance againstthe rotation of the rotor 71 in its rotational direction, generated bythese magnetic fluxes crossing the windings 82, disappear. The rotor canrotate in a high speed, accordingly.

Also, similarly, the magnetic fluxes from the magnets 79 do not flowinto the windings of the respective first teeth 81. Thus, the torque tobe generated between the electrified first teeth 81 and the magnets 79and then given to the rotor 71 is lowered. That is, the low torque highspeed operation is realized.

As thus described, simply, the second teeth reciprocally move betweenthe position at which the second teeth directly oppose the first teethand the other position at which the second teeth are placed midwaybetween adjacent first teeth. The entire structure thus can be compact.

Now, a space making the magnetic resistance, i.e., a gap (“j,”“k,”“m,”“n” and so on) that causes the magnetic resistances is described.The gap that causes the magnetic resistance is defined as a magneticresistance space of air or the equivalent. The gap that causes themagnetic resistance (hereunder, simply called gap) is further described.

FIGS. 14( a) to (e) are illustrations for describing differences betweena contact area which varies a magnetic resistance between two membersand a gap. Generally, it is known that, when a magnetic flux flow comingfrom a magnet is going to flow between the two members made of amagnetic material, if any portion is ensured to be a flow route for themagnetic fluxes, the magnet does not provide any surplus magneticfluxes. When the two members are completely separated by a gap, themagnet tries to make the magnetic fluxes flow by any means, and themagnetic fluxes start to flow from a portion that gives the easiestroute, i.e., from the narrowest gap.

FIG. 14( a) shows a condition under which two magnetic members 101 and102 configured as the letter L in their cross sections are tightlycoupled with each other. A vertical cross section of the major portionof the magnetic member 101 has an area A, while a vertical cross sectionof a projection of the magnetic member 101 has an area B. Also, avertical cross section of the major portion of the magnetic member 102has an area D, while a vertical cross section of a projection of themagnetic member 102 has an area D-B. A horizontal cross section of therespective projections has an area C, which is the same as one another.

Now, the following conditions are given: area A=area D=area C=200 S, andarea B=50 S. Also, it is decided that magnetic fluxes 103 coming from amagnet out of the illustration flow to the magnetic member 102 from themagnetic member 101.

Suppose that, as shown in FIG. 14( b), the two magnetic members 101 and102 move to be relatively separated from one another by the respectivedistances a and b (a=b) at the area B portion of the vertical crosssection and the area D-B portion of the vertical cross section, whilethe area C portions of the horizontal surfaces are in slide contact witheach other. Upon this movement, because a space of the distance b ismade between the two magnetic members 101 and 102, the magnetic fluxflow flowing into the major portion of the magnetic member 101 havingthe area A=200 S becomes saturated at the area B portion, and reducesthe magnetic flux flow that flows through the area B=50 S. This magneticflux flow 103 flows into the magnetic member 102 via the slidingsurfaces C1 (area C1=150 S, B<C1).

Next, suppose that, as shown in FIG. 14( c), the two magnetic members101 and 102 further move to be relatively separated from one another bythe respective distances 2 a and 2 b at the area B portion of thevertical cross section and the area D-B portion of the vertical crosssection, while the area C portions of the horizontal surface are inslide contact with each other. In this situation, the magnetic flux flowbecoming saturated at the area B portion also reduces to the magneticflux flow that flows through the area B=50 S, and flows into themagnetic member 102 via the sliding surfaces C2 (area C2=100 S, B<C2).

That is, no magnetic resistance changes between conditions of FIG. 14(b) and FIG. 14( c). Specifically, the spaces that separate the twomagnetic members 101 and 102 by the distances a, b or 2 a, 2 b in themagnetic flux direction are not spaces for causing the magneticresistance, because the magnetic resistance does not change (is notvaried), even though the distances change. Namely, the spaces are notgaps.

Further, suppose that, as shown in FIG. 14( d), the two magnetic members101 and 102 further move to be relatively separated from one another bythe respective distances 3.5 a and 3.5 b at the area B portion of thevertical cross section and the area D-B portion of the vertical crosssection, while the area C portions of the horizontal surface are inslide contact with each other. On this occasion, each area C portion ofthe respective horizontal surface has a sliding surface area C3=25 S.That is, the following relationship is given: B>C3. Thus, the magneticflux flow 103 is saturated at the sliding surface C3, and the magneticflux flow corresponding to the area 25S flows into the magnetic member102.

That is, the magnetic resistance between the two magnetic members 101and 102 changes for the first time when the area of the sliding surfaceC becomes smaller than the area B of the vertical cross section of theprojection of the magnetic member 101. In other words, the magneticresistance changes depending on the change of each area of the slidingsurfaces between the two members.

The change of the magnetic resistance shown in FIGS. 14( c) and (d) isnot caused by the changes of the separating distances between the twomembers (the changes 2 a and 2 b to 3.5 a and 3.5 b), but by the changeof the area of the sliding surface C (the change of C2 to C3). Namely,the separating distances 3.5 a and 3.5 b that have changed still do notcause the gaps.

Also, FIG. 14( e) shows a condition under which the two magnetic members101 and 102 are relatively separated from one another by the respectivedistances 5 a and 5 b at the area B portion of the vertical crosssection and the area D-B portion of the vertical cross section, so thatthe sliding surfaces C3 are completely released from the abuttingfunction to be separated by the distance C4.

As described above, when the two members are completely separated by agap, the magnetic flux flow of the magnet flows through a portion thatgives the easiest route, i.e., through a portion having the narrowestdistance C4. Namely, the magnetic resistance is generated at the portionhaving the distance C4, and the distance C4 is a magnetic resistancegap. That is, the magnetic resistance varies in accordance with thechange of the distance C4.

In other words, the distance C4 is a gap to vary the magneticresistance. However, the distances 5 a and 5 b are not spaces to varythe magnetic resistance, i.e., those are not gaps. Any portion that isdescribed as a gap in this embodiment is the portion that defines thedistance C4 discussed above.

In the present embodiment, as thus described, the stator is divided intoat least two portions, and one portion is moved at right angles to therotational direction of the rotor, i.e., to the direction of themagnetic flux flow that flows into each core around which the respectivewinding is wound from the rotor to form the variable gaps, to therebygreatly change the output characteristic of the rotary electricalmachine without consuming the electric power that does not contribute tothe torque.

FIGS. 15( a) and (b) show a structure of the major part of analternative of the axial gap type electric motor in the firstembodiment.

FIG. 15( a) shows a condition that is the same as the condition shown inFIG. 13( a), under which each first tooth 81, of the first statorsection 83 directly opposes the respective second tooth 84 of the secondstator section 87. From this condition, each second tooth 84 in thisembodiment obliquely moves downward to be separated from the respectivefirst tooth 81 as indicated by the two-headed arrow “e” of theillustration. That is, as shown in FIG. 15( b), the second statorsection 87 moves in a direction parallel to the rotational direction ofthe rotor 71 that exists out of the illustration and also moves in adirection perpendicular to the rotational direction of the rotor 71.

Thus, a distance, between each first tooth 81 of the first statorsection 83 and the respective second tooth 84 of the second statorsection 87, and in the direction perpendicular to the rotationaldirection of the rotor 71, changes from a distance “p” shown in FIG. 15(a) to a distance “p′” shown in FIG. 15 (b) (p′>p). That is, a magneticresistance gap between each first tooth 81 and each second tooth 84 islarger than that in the structure shown in FIG. 13( b). Therefore, theoutput characteristic of the electric motor can vary on a larger scale.

FIGS. 16( a) to (d) show a structure of the major part of anotheralternative of the axial gap type electric motor in the firstembodiment.

As shown in FIGS. 16( a) and (b), each first tooth 104 has a protrudingportion 104-1 abutting on a side surface of the respective second tooth105 and an end surface that opposes one end surface of the second tooth105. Each first tooth 104 therefore prohibits the respective secondteeth 105 from moving rightward beyond the right opposing positionsshown in FIG. 16 (b).

In this embodiment, each second tooth 105 also not only moves in thedirection parallel to the rotational direction of the rotor 71 thatexists out of the illustration but also moves in the directionperpendicular to the rotational direction of the rotor 71. That is, eachsecond tooth 105 obliquely moves downward to be separated from therespective first tooth 81.

FIG. 16( c) shows an alternative in which each second tooth 105 moveshorizontally as indicated by the arrow “f,” while FIG. 16( d) showsanother alternative in which each second tooth 105 obliquely movesdownward as indicated by the arrow “g.”

In this alternative, also a magnetic resistance gap between each firsttooth 104 and each second tooth 105 is larger than that in the structureshown in FIG. 13( b). Therefore, the output characteristic of theelectric motor can vary on a larger scale.

Structure and Operation of an Axial Gap Type Electric Motor According toa Second Embodiment

FIGS. 17( a) to (d) show a structure of the major part of an axial gaptype electric motor in a second embodiment.

As shown in FIGS. 17( a) and (c), each first tooth 106 in thisembodiment is formed in such a manner that a portion lower than an endportion 106-1 facing the annular section 74 of the rotor 71 includes awinding-possessing-portion 106-2 having a winding 107 positioned aroundit and a non-winding-possessing portion 106-3 having no windingpositioned around it.

In this connection, as shown in FIGS. 17( b) and (c), each second tooth108 is divided into an inner tooth portion 109 corresponding to thewinding-possessing-portion 106-2 of the respective first tooth 106 andan outer tooth portion 110 corresponding to thenon-winding-possessing-portion 106-3 of the each first tooth 110.

The inner tooth portion 109 of each second tooth 108 is placed at aninner side (side radially closer to the center axis) of the annularretainer 111, while the outer tooth portion 110 is placed at an outerside of the retainer 111 and at a middle position between two adjacenttooth portions 109.

A condition shown in FIG. 17( c) is the same as the condition shown inFIG. 13( a), because the winding-possessing-portion 106-2 of each firsttooth 106 and the inner tooth portion 109 of each second tooth 108directly oppose each other. Also, because thenon-winding-possessing-portion 106-3 and the outer tooth portion 110 areplaced at the outer side of the circular arrangement and are alternatelypositioned, the magnetic gap is extremely large, and they nearly do notaffect the magnetic flux flow.

On the contrary, a condition shown in FIG. 17( d) is the same as thecondition shown in FIG. 13( b) regarding a positioning relationshipbetween the winding-possessing-portion 106-2 of each first tooth 106 andthe inner tooth portion 109 of each second tooth 108 a. Eachnon-winding-possessing portion 106-3 and the respective outer toothportion 110 directly oppose to each other.

That is, the magnetic fluxes of each field magnet 79 flow through therespective non-winding-possessing portion 106-3 and outer tooth portion110 and the retainer 111, and nearly do not flow through thewinding-possessing-portion 106-2 of each first tooth 106. Namely, themagnetic fluxes of each winding-possessing-portion 106-2 can be shut offstronger than the embodiment shown in FIG. 13( b).

Additionally, in the first and second embodiments, the opposing surfacesof the rotor and the stator, and the opposing surfaces of the statorsections, which are the two portions of the divided stator, are arrangedto extend parallel to (horizontally in the illustrations) the rotationalsurface of the rotor; however, the opposing surfaces of those componentsare not limited to such parallel arrangement.

FIGS. 18( a) and (b) show a further alternative wherein the opposingsurfaces of the rotor and the stator, and the opposing surfaces of thestator sections, which are the two portions of the divided stator,extend slantwise in the axial direction.

In the alternative shown in FIGS. 18( a) and (b), the respectiveopposing surfaces of the field magnets 113 retained by the retainer 112,the first teeth 114, and the second teeth 116 retained by the retainer115 extend upward outward relative to the center 117 of the rotor 112 inits radial direction. With this alternative structure, the same actionsand effects can be obtained as those in the first and secondembodiments.

Structure of a Radial Gap Type Electric Motor According to a ThirdEmbodiment

FIG. 19 is a cross sectional view, showing a structure of a radial gaptype electric motor according to a third embodiment.

Additionally, in the illustration, in order to simply show the thirdembodiment in comparison with the first embodiment, components havingthe same functions are assigned with the same reference numerals asthose assigned in FIG. 10.

As shown in the illustration, this radial gap type electric motorincludes a cylindrical rotor 73 rotating about an axis of a rotationalshaft (indicated by a rotational center 117 in the illustration), and afirst stator core 83 positioned inside of the cylindrical rotor 73 andhaving a plurality of first teeth 81, one end surfaces of which opposeto the rotor 73. A winding 82 is wound around a circumferential sidesurface of each first tooth 81 except for both the end surfaces 81 a and81 b thereof.

The electric motor further includes a second stator core 87 having aplurality of second teeth 84. Each second tooth 84 has one end surface84 a positioned to oppose the end surface of the first tooth 81 thatfaces in an opposite direction from the rotor 73. The second tooth 84also has another end surface 84 b retained in a retainer 85.

In this radial gap type electric motor, the second stator core 87 movesat right angles to a direction of flow of magnetic fluxes that aregenerated, when the magnetic windings 82 of the first stator core 83 areelectrified, to permeate through the respective first teeth 81, i.e.,clockwise or counterclockwise in the illustration. Therefore, the samefield magnet control as that described with reference to FIGS. 13( a)and (b) can be practicable.

Structure of a Radial Gap Type Electric Motor According to a FourthEmbodiment

FIG. 20 is a cross sectional view, showing a structure of a radial gaptype electric motor according to a fourth embodiment.

Additionally, also in the illustration, in order to simply show thefourth embodiment in comparison with the first embodiment, componentshaving the same functions are assigned with the same reference numeralsand symbols as those assigned in FIG. 10.

As shown in the illustration, this radial gap type electric motorincludes a columnar or cylindrical rotor 73 rotating about a rotationalshaft 72, and a first stator core 83 positioned outside of the rotor 73in its radial direction. The first stator core 83 has a plurality offirst teeth 81, one end surfaces of which oppose the rotor 73. A windingis wound around a circumferential side surface of each first tooth 81,except for both the end surfaces 81 a and 81 b thereof.

The electric motor further includes a second stator core 87 having aplurality of second teeth 84. Each second tooth 84 has one end surface84 a positioned to oppose the end surface 81 b of the first tooth 81that faces in a direction opposite the rotor 73. The second tooth alsohas also an other end surface 84 b retained in a retainer 85.

In this radial gap type electric motor, the second stator core 87 movesat right angles to a direction of flow of magnetic fluxes that aregenerated when the magnetic windings 82 of the first stator core 83 aresupplied with the electric power and permeates through the respectivefirst teeth 81, i.e., clockwise or counterclockwise in the illustration.Thus, the same field magnet control as that described with reference toFIGS. 13( a) and (b) can be practicable.

Structure of an Axial Gap Type Electric Motor According to a FifthEmbodiment

FIG. 21 is a perspective view, showing the major part of an axial gaptype electric motor according to a fifth embodiment.

This illustration only shows a rotor of the axial gap type electricmotor of this embodiment.

As shown in FIG. 21, first, the rotor 120 of this embodiment includes aplurality of field magnets 122 fixedly positioned on a annular section121 of a rotor yoke of a first rotor section 120-1.

Next, the rotor 120 includes a second rotor section 120-2 constructed insuch a manner that magnetic members 123, which number is the same as thenumber of the field magnets 122, are disposed on a rotary retainer (notshown) to nearly slidably contact with a rotational surface of eachfield magnet 122, and the second rotor section 120-2 coaxially engageswith the first rotor section 120-1 and rotates together with the firstrotor section 120-1.

A stator that is positioned to oppose to the rotor 120 has the samestructure as that of the stator 39 shown in FIGS. 3 and 4.

In this axial gap type electric motor of this embodiment, when it makesa low speed high torque rotation, as shown in FIG. 21, the first rotorsection 120-1 and the second rotor section 120-2 are positioned in sucha manner that the respective field magnets 122 and the magnetic members123 entirely overlap with each other to rotate in phase.

Thereby, magnetic fluxes of the field magnets 122 are controlled togather in the respective magnetic members 123 and then flow into teethof the stator.

FIG. 22 is an illustration, showing a relationship of displacement ofthe rotational phase between the first rotor section 120-1 and thesecond rotor section 120-2 when the rotor 120 makes a high speed lowtorque rotation in the structure. FIG. 22 shows a condition under whichthe displacement of the rotational phase between the first rotor section120-1 and the second rotor section 120-2 is the maximum.

The first rotor section 120-1 and the second rotor section 120-2 canmove relative to each other between the condition under which the phasesare consistent with one another as shown in FIG. 21 and the conditionunder which the phases are displaced within 15 degrees from one anotheras shown in FIG. 22.

Under the condition that the phases are displaced with 15 degrees asshown in FIG. 22, a magnetic gap between each field magnet 122 and therespective magnetic member 123 becomes extremely large at large portionsin a width direction of the rotational shaft, except for a relativelysmall gap partially formed at end portions located close to therotational center. Thus, almost the entire magnetic flux flow of eachfield magnet 122 flow through the neighboring field magnet 122 via theannular section 121 to reflux.

The magnetic flux flow that flows into the magnetic member 123 throughthe small gap formed at the portions close to the rotational center isan extremely small portion of the entire magnetic flux flow. Also, themagnetic gap between each magnetic member 123 and the respective toothof the stator becomes extremely large at large portions in the widthdirection of the rotational shaft, except for a relatively small gappartially formed at end portions located close to the rotational center.

Thus, the magnetic flux flow that slightly flows into each magneticmember 123 from the respective field magnets 122 does not flow throughthe tooth of the stator. Thereby, the drive condition during the highspeed low torque rotation can be realized.

In other words, by suitably positioning the first rotor section and thesecond rotor section to control the displacement of the rotational phasefrom the state shown in FIG. 22 to the state shown in FIG. 23, an amountof the flux linkage is controlled. The relationship between therotational speed and the rotational torque thus can be controlledwithout wastefully using the electric power.

Structure of an Axial Gap Type Electric Motor According to a SixthEmbodiment

FIG. 23 is an illustration, showing a structure of the major part of theaxial gap type electric motor according to a sixth embodiment.

This illustration only shows a rotor of the axial gap type electricmotor of this embodiment.

As shown in FIG. 23, first, the rotor 124 of this embodiment includes aplurality of magnet members 126 fixedly positioned on an annular section125 of a rotor yoke of a first rotor section 124-1.

Next, the rotor 120 includes a second rotor section 124-2 constructed insuch a manner that magnetic-member-combined type magnets 129, whichnumber is the same as the number of the magnetic members 126, aredisposed on a rotary retainer (not shown) to nearly slidably contactwith a rotational surface of each magnetic member 126, and the secondrotor section 124-2 coaxially engages with the first rotor section 124-1and rotates together with the first rotor section 124-1.

Each magnetic-member-combined type magnet 129 is formed in such a mannerthat a magnetic member 127 disposed to oppose to the respective magneticmember 126 and a field magnet 128 disposed to oppose to the stator (notshown) are stacked with each other.

A stator that is positioned to oppose to the rotor 124 has the samestructure as that of the stator 39 shown in FIGS. 3 and 4.

In this axial gap type electric motor of this embodiment, when it makesa low speed high torque rotation, as shown in FIG. 23, the first rotorsection 124-1 and the second rotor section 124-2 are positioned in sucha manner that the respective magnetic members 126 and themagnetic-member-combined type magnets 129 entirely overlap with eachother to rotate in phase.

Thereby, the magnetic fluxes coming from one magnetic pole of each fieldmagnet 128 are gathered and the flow thereof is adjusted by the combinedtype magnetic member 127 and the magnetic member 126 positionedthereabove and opposing to the combined type magnetic member 127. Themagnetic fluxes are then again gathered and the flow thereof is againadjusted by the annular section 125, the neighboring magnetic member 126and the magnetic member 127 positioned opposite and below the magneticmember 126. Afterwards, the magnetic fluxes flow through the magneticmember 127 and the combined type field magnet 128.

The magnetic fluxes coming from the other magnetic pole of each fieldmagnet 128 flow into each tooth of the stator opposing to the fieldmagnet 128 positioned therebelow, and flow through the neighboring toothvia the stator side yoke.

That is, the magnetic fluxes of each field magnet 128 flow through therespective combined magnetic member 127 and magnetic member 126, theannular section 125, the neighboring magnetic member 126, the magneticmember 127 opposing to the magnetic member 126, the combined type fieldmagnet 128 combined with the magnetic member 127, the tooth of thestator, the stator side yoke, the adjacent tooth, and the combined typefield magnet 128 opposing the adjacent tooth to reflux through the coilwound around the tooth of the stator.

This condition is the same as the condition of the flow of the magneticflux flow shown in FIG. 13( a). Thereby, the drive condition during thelow speed high torque rotation is made can be realized.

FIG. 24 is an illustration, showing a relationship of displacement ofthe rotational phase between the first rotor section 124-1 and thesecond rotor section 124-2 when the rotor 120 makes a high speed lowtorque rotation in the structure. FIG. 24 shows a condition under whichthe displacement of the rotational phase between the first rotor section120-4 and the second rotor section 120-4 is the maximum.

In this embodiment, the first rotor section 124-1 and the second rotorsection 124-2 can move relative to each other between the conditionunder which the phases are consistent with one another as shown in FIG.23 and the condition under which the phases are displaced within 15degrees from one another as shown in FIG. 24.

Under the condition that the phases are displaced with 15 degrees asshown in FIG. 24, a magnetic gap between each magnetic member 127 andthe respective magnetic member 126 is extremely large. Thus, almost themagnetic flux flow of each magnetic member 127 does not flow into themagnetic member 126, i.e., the magnetic flux flow is under the shut outcondition.

This condition is slightly different from the condition shown in FIG.13( b); however, the condition under which the gap becomes larger at aportion where the magnetic flux flow has been gathered and adjustedbefore, and the magnetic flux is shut out not to flow through the toothof the stator side yoke is the same as the condition of FIG. 13( b).Thereby, the drive condition during the high speed low torque rotationis made can be realized.

In other words, by suitably positioning the first rotor section 124-1and the second rotor section 124-2 to control the displacement of therotational phase from the state shown in FIG. 23 to the state shown inFIG. 24, an amount of the flux linkage is controlled. The relationshipbetween the rotational speed and the rotational torque thus can becontrolled without wastefully using the electric power.

According to the present invention, a robust and small rotary electricalmachine can be advantageously provided which has a mechanism capable ofvarying an output characteristic without enlargement of the wholemachine configuration, without increase of mechanical loss, without anytransmission, and without consumption of electric power that does notcontribute to increasing torque.

Although this invention has been disclosed in the context of a certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while a number of variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or subcombinations of the specific featuresand aspects of the embodiments may be made and still fall within thescope of the invention. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can be combinewith or substituted for one another in order to form varying modes ofthe disclosed invention. Thus, it is intended that the scope of thepresent invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims.

1. An electric motor comprising: a rotor arranged to rotate about anaxis of a rotating shaft, the rotor including a plurality of permanentmagnets; and a stator arranged so as to oppose the rotor, the statorincluding a plurality of stator sections each including a winding;wherein each of the plurality of the stator sections is divided into atleast two stator sections including a first stator section including afirst end portion arranged to oppose the plurality of permanent magnetsand a second end portion opposite to the first end portion, and a secondstator section; one of the first stator section and the second statorsection is movable relative to the other of the first stator section andthe second stator section to change a magnetic resistance between thefirst stator section and the second stator section; a relative movementof the first stator section and the second stator section changes amagnetic flux flowing through the rotor and the stator between a firstmagnetic flux flow state and a second magnetic flux flow state; thefirst magnetic flux flow state is defined by a magnetic resistancebetween adjacent first end portions of adjacent ones of the first statorsections being larger than a magnetic resistance between the second endportion of the first stator section and the second stator section suchthat a magnetic flux between adjacent permanent magnets flows throughthe adjacent ones of the first stator sections via adjacent ones of thesecond stator sections so as to hardly allow the magnetic flux to flowthrough a space between the adjacent first end portions of the adjacentones of the first stator sections; and the second magnetic flux flowstate is defined by a magnetic resistance between the adjacent first endportions of the adjacent ones of the first stator sections being smallerthan a magnetic resistance between the second end portion of the firststator section and the second stator section such that a magnetic fluxbetween the adjacent permanent magnets flows through the adjacent firstend portions of the adjacent ones of the first stator sections so as tohardly allow the magnetic flux to flow through the first stator sectionsvia the second stator sections.
 2. The electric motor as recited inclaim 1, wherein in each of the plurality of the stator sections, afirst end surface of the first end portion of the first stator sectionis larger than a second end surface of the second end portion of thefirst stator section such that a gap between the adjacent first endportions of the adjacent ones of the first stator sections is smallerthan a gap between adjacent second end portions of the first statorsections.
 3. The electric motor as recited in claim 1, wherein in eachof the plurality of the stator sections, a first end surface of thefirst end portion of the first stator section is larger than a secondend surface of the second end portion of the first stator section suchthat a magnetic resistance between the adjacent first end portions ofthe adjacent ones of the first stator sections is smaller than amagnetic resistance between adjacent second end portions of the firststator sections.
 4. The electric motor as recited in claim 1, wherein ineach of the plurality of the stator sections, a first end surface of thefirst end portion of the first stator section is larger than a secondend surface of the second end portion of the first stator section suchthat a magnetic resistance between the adjacent first end portions ofthe adjacent ones of the first stator sections is larger than a magneticresistance between the first end portion of the first stator section andthe permanent magnet adjacent to the first end portion of the firststator section.
 5. The electric motor as recited in claim 1, wherein thesecond end portion of the first stator section opposes the second statorsection.
 6. The electric motor as recited in claim 1, wherein therelative movement of the second stator section and the first statorsection includes a reciprocal movement within a predetermined angle in arotational direction of the rotor.
 7. The electric motor as recited inclaim 1, wherein the first stator section includes first teeth on whicha winding is provided, the second stator section includes second teethincluding a first end surface opposed to the second end portion of thefirst stator section, and one of the first stator section and the secondstator section moves in a rotational direction of the rotor or adirection opposite to the rotational direction.
 8. The electric motor asrecited in claim 7, wherein a rotational angle of the first statorsection relative to the second stator section is less than a pitch angledefined by adjacent second teeth of the second stator section arrangedin the rotational direction of the rotor.